Thanks for your reply, that makes sense at a glance... But wait, you CAN still mine BTC, you just have to keep getting newer equipment to stay in front of the pack. I assume Moore's law will keep better mining equipment coming and coming (perhaps even at a steady cost), as the mining difficulty keeps increasing... So, I'm not sure I quite buy the simplicity of this theory. It seems more to me that the price of BTC will determine how much people want to invest in mining, rather than the other way around. My sense is the price is much more affected by many many issues that are unrelated to the newest mining equipment.

I'm speaking as someone who only only knows the very basics, and I have zero mining experience, so I'm happy to learn from those who think I'm seeing it incorrectly.